Historically, many lighting system luminaires have relied upon a single light source and single primary reflector and in some implementations, a single final primary diffuser or “window” that surrounds the light source and creates some type of illumination pattern, such as spot light or area light depending upon the photometric needs in a given application. The light source was generally a nominally 4 pi steradian emitter from either a filament or an electric discharge arc contained in one, or more, volumetric enclosures (e.g., light bulbs.) Given the lack of control over the spatial emission pattern and fixed spectral content inherent in the underlying technologies, the luminaire designer has usually relied upon the creation of a fairly large proximate optical system around the light source to achieve a desired, relatively invariant photometric distribution. This single light source to one function paradigm has prevailed in the lighting industry for well over a century.
With the advent of high efficiency light-emitting diode (LED) sources, as known in the art, it is possible to obtain large light flux packages including LED die material (e.g., about 1 mm2) along with an appropriate wavelength converting material (e.g., phosphor) placed in proximity to the die to create a composite light spectrum that is close to the Planckian locus. As commonly known in the art, the Planckian locus is also referred to as the black body locus, which mathematically refers to the set of points that characterize light emitted by a black body radiator as a function of the temperature of the black body in a particular chromaticity coordinate space. These packages are now showing efficacies in the range of 150 lumens/watt such that, for example, a 1 watt device can be capable of producing 150 lumens of light or about ¼th of the flux of a standard 60 watt incandescent lamp. If these individual sources are differentiated and/or operated differentially then it is possible to piecewise electronically parse a previously larger lighting function into smaller functions in both spectral and spatial respects.
Arrays of powerful compact LED dies or array packages are also available that can provide high granularity of control as desired for various applications. Some LED dies can have a high current density with high surface exitance in the shorter wavelength blue, or even ultraviolet, regions of the spectrum such that high optical energy densities can be achieved with less than 0.2 mm2 of material, for example. As epitaxial materials improve in terms of external quantum efficiencies and energy densities, smaller elements of light can be harnessed in efficient optical structures.
Therefore, a reduction in the size of the finished optical structure is possible, and hence the etendue of the light source which can be advantageously used to create better optically controlled systems using less material at much lower costs to the final application. The use of an LED is but one example of a “light emitting element” otherwise known as an “LEE” which includes Light Emitting Diodes, laser diodes, superluminescent diodes, or organic light emitting diodes and other compact semiconducting devices as are known in the art.